The purpose of this study is to determine the effects of low-and high-intensity exercise training on the slow component of oxygen uptake kinetics during 20 minutes of constant-load exercise. Two groups of subjects will train 3 days per week for 6 weeks, one at an intensity above their lactate threshold and one at an intensity below their lactate threshold. Before and after training each subject will perform 20 minutes of constant-load exercise; oxygen uptake will be monitored and cardiac output will be determined by echocardiographic procedures.